JavaScript in Operator

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The in operator is an inbuilt operator in JavaScript which is used to check whether a particular property exists in an object or not. It returns a boolean value true if the specified property is in an object, otherwise, it returns false.

Syntax:

prop in object

Parameters: This function accepts the following parameter as mentioned above and described below:

prop: This parameter holds the string or symbol that represents a property name or array index.
object: This parameter is an Object which is to be checked whether it contains the prop.

Return value: This method returns a boolean value:

true: The value true is returned if the specified property is found in an object.
false: The value false is returned if the specified property is not found in an object.

Example 1: Below is an example of the in-operator.

Javascript

<script> 
    function gfg() { 
    // Illustration of in operator 
    const array = ['zambiatek', 'for', 
                'zambiatek'] 
      
    // Output of the indexed number 
    console.log(0 in array); 
      
    // Output of the Value 
    console.log('for' in array); 
      
    // output of the Array property 
    console.log('length' in array); 
    } 
    gfg(); 
</script>

Output:

true
false
true

Example 2: This example shows the use of the in operator in Javascript.

Javascript

<script> 
    // Illustration of in operator 
    const array = ['zambiatek', 'zambiatekfor', 
                'zambiatek', 'zambiatek1'] 
      
    // Output of the indexed number 
    console.log(0 in array)         
    console.log(2 in array)     
    console.log(5 in array)     
      
    // Output of the Value 
    console.log('for' in array) 
    console.log('zambiatek' in array) 
      
    // output of the Array property 
    console.log('length' in array) 
</script>

Output:

true
true
false
false
false
true

Example 3: This example shows the use of the in operator in Javascript.

Javascript

<script> 
    // Illustration of in operator 
    const object = { val1: 'Geeksforzambiatek', 
                    val2: 'Javascript', 
                    val3: 'operator', 
                    val4: 'in' }; 
      
    console.log('val1' in object); 
      
    delete object.val1; 
    console.log('val1' in object); 
      
    if ('val1' in object === false) { 
    object.val1 = 'GEEKSFORGEEKS'; 
    } 
      
    console.log(object.val1); 
</script>